AB5 type hydrogen storage alloys have been the predominant materials for anodes of rechargeable batteries. For improved battery performance, the alloys are required to have various properties, such as hydrogen storage capacity, equilibrium pressure, corrosion resistance, and flatness of the plateau. Some of these properties conflict with each other, so that studies have been made for improving one property without sacrificing the other. For example, studies have been made on additional elements and compositions of the hydrogen storage alloys. However, the additional elements increase the number of constitutional elements of the alloy, which adds to the difficulties in and the cost of the battery recycling, raising new problems.
For the purpose of improving the activities of hydrogen storage alloys, which is a factor in improved activities of the batteries, there have been proposed to treat the alloy surface with acid or alkali, or to increase the content of the A-site components. However, the activities of the alloy conflict with the corrosion resistance, and these methods for improving the activities thus simultaneously impair the corrosion resistance.
In the art of metal hydride-hydrogen batteries, electrode active materials that satisfy both of these conflicting properties have been under development. To this end, there is proposed to mix an alloy excellent in corrosion resistance and an alloy excellent in activities, for preparing starting materials for the active materials. However, such alloys excellent in different properties used in this method are also different in their compositions or structures, or obtained by totally different production methods. Thus, even though the activities and the corrosion resistance are improved, the capacity and the internal pressure characteristics of the batteries are lowered, or the costs for recycling the batteries are disadvantageously increased.